1. Field of the Invention
This invention relates to a radiation image read-out apparatus, and more particularly to a radiation image read-out apparatus which obtains image data representing a radiation image recorded on each radiation image convertor panel recorded by exposing a plurality of radiation image convertor panels to radiation with the radiation image convertor panels superposed one on another.
2. Description of the Related Art
When certain kinds of phosphors are exposed to radiation such as X-rays, they store a part of energy of the radiation. Then when the phosphors which have been exposed to the radiation are exposed to stimulating light such as visible light, light having a wavelength shorter than the stimulating light is emitted from the phosphors in proportion to the stored energy of the radiation. Phosphors exhibiting such properties are generally referred to as “stimulable phosphors”. In this specification, the light emitted from the stimulable phosphors upon stimulation thereof will be referred to as “stimulated emission”. There has been known as a CR (computed radiography) a radiation image recording and reproducing system, comprising a radiation image recording apparatus and a radiation image read-out apparatus, in which a layer of the stimulable phosphors is exposed to a radiation passing through an object such as a human body to have a radiation image of the object once stored on the stimulable phosphor layer as a latent image, stimulating light such as a laser beam is subsequently projected onto the stimulable phosphor layer, and the stimulated emission emitted from the stimulable phosphor layer is photoelectrically detected, thereby obtaining an image signal (a radiation image signal) representing a radiation image of the object. There has been known a radiation image convertor panel comprising a stimulable phosphor layer formed on a substrate as a recording medium employed in the radiation image recording and reproducing system.
The apparatus for obtaining image data (image signal) representing a radiation image of the object includes those which operate in various systems. For example, there has been known an apparatus in which a pair of radiation image convertor panels superposed one on the other with a copper plate or the like absorbing radiation intervening therebetween are exposed to radiation passing through an object so that low energy components of the radiation are more absorbed by the radiation image convertor panel nearer to the object, whereby a low energy radiation image of the object is recorded on the radiation image convertor panel, and high energy components of the radiation are more absorbed by the radiation image convertor panel remoter from the object, whereby a high energy radiation image of the object is recorded on the radiation image convertor panel, the pair of radiation image convertor panels are separated from each other so as not to be deformed, and stimulated emission emitted from each of the radiation image convertor panels upon exposure to stimulating light is detected by the use of a photodetector exclusive to the radiation image convertor panel, thereby obtaining two pieces of image data respectively representing a low energy radiation image and a high energy radiation image of the object. See, for instance, Japanese Patent Nos. 2561156 and 2835622.
Further, there has been known the fact that high quality radiation image information representing a radiation image of the object by an operation involving the two pieces of image data respectively representing a low energy radiation image and a high energy radiation image of the object. As such an operation, there have been known a so-called energy subtraction processing for extracting a particular structure in the object or a so-called superposition processing for clearly showing slight differences in absorption of the radiation in the object.
However, the conventional apparatus in which the two pieces of image data are obtained from a pair of radiation image convertor panels superposed one on the other is disadvantageous in that the overall size of the apparatus is increased as compared with an apparatus in which a single piece of image data is obtained from a single radiation image convertor panel since the stimulated emission emitted from each of the radiation image convertor panels is detected by the use of a photodetector exclusive to the radiation image convertor panel.